Stress orientations from hydraulic fracturing tests in the Ruhr area in comparison to stress orientations from borehole observations and earthquake focal mechanisms

To gain information on the regional tectonic state of stress in an area it is important to separate it from stresses affected from anthropogenic activities such as the construction of tunnels or mines. The Ruhr region is characterised by centuries of mining. To ensure safe operations, large-scale hydraulic fracturing campaigns were carried out in several mines at the end of the last century. This study provides a compilation of the regional state of stress in the Ruhr area based on the mine measurements which have been reassessed to deduce the regional stress component and to compare that with stress orientations from independent sources (deep borehole stress information and earthquake focal mechanisms). As orientations of both data sets agreed well the selected stress data of the mines have been combined with the borehole and earthquake data and a mean orientation of the maximum horizontal stress, S-Hmax, of N154 degrees was obtained for the Ruhr area. The spatial distribution of the stress orientations in the Ruhr area shows a rather homogeneous stress pattern with only very few locations where stress orientations differ significantly from the average.